The effect of tin on gastric secretion in rats was examined. The volume, acidity, and total acidity of gastric contents showed a remarkable reduction in rats administered orally with tin (3.0mg/100g body weight) during 3 days. Also, acidity and total acidity of gastric contents in rats that had fasted for 24 hours significantly decreased 6 hours after a single oral administration of tin (3.0mg/100g). An oral administration of tin to rats that had fasted for 24 hours diminished the acidity and total acidity of gastric contents with the three dose (1.5, 3.0 or 5.0mg of Sn/100g) of tin employed, while did not alter the volume. On the other hand, the volume, acidity, and total acidity of gastric contents in rats that had fasted for 24 hours significantly reduced 1 hour after a single intraperitoneal injection of tin (3.0mg/100g), while it had no effect after 6 hours of fasting. The present study indicates that tin inhibits gastric secretion of rats.